https://www.cnet.com/news/trailer-for-netflix-roma-has-no-spoilers-or-anything-else-alfonso-cuaron/

Cuarón's follow-up to his Oscar win for Gravity is a semi-autobiographical Spanish-language film set in Mexico City in the early 1970s. You won't get that from the trailer, however, which simply shows a minute of water washing over tiles while a plane flies overhead. The only thing the mesmeric clip really tells us about the film is that it's black-and-white.

A black-and-white foreign-language film with no stars? That would make any Hollywood marketing department nervous, which is probably why they've chosen to build mystique rather than showing too much.